The purpose of this project was to study the interaction of polycyclic aromatic hydrocarbons (PAH) (specifically benzo(a)pyrene and 7,8-dihydro-7,8-dihydroxybenzo(a)pyrene) with RNA and protein from rat liver and lung microsomes. PAH were incubated with microsomal preparations, and PAH and metabolites bound to RNA and protein were solubilized and isolated by solvent extraction followed by thin layer and column chromatography and gel electrophoresis. Similar metabolites of PAH are formed by both liver and lung, although liver appears to be metabolically more active than lung for metabolism of the PAH studied.